Quote:
Originally Posted by serialk11r
I don't think that explains it, at least not all of it. Almost all of the supercars have MORE plan taper at the greenhouse than the low-drag cars you mentioned. They also have side ducting that vents into the wake, which gets rid of some of the drag that comes from the wider rear.
The Veyron's rear has no taper to speak of, so that's probably bad. As someone else mentioned, the Hennessey Venom is just some Elise parts made a little bigger and slapped together, no surprise there (speaking of Lotus, the Exige comes from the factory with a ton of drag and not much downforce too). I also doubt that Koenigsegg does much careful aero optimization.
The areas I see on supercars that more drag comes from are:
1. Inlet scoops (fairly common, but are mostly pretty small and I don't imagine they add too much drag)
2. More radiators, other cooling ducts
3. Fat tires
4. Wings, canards, and other aero add-ons
5. Subtle things like the diffuser being angled higher to provide more downforce and more drag.
Without these things, I think the basic supercar shape (nearly perfectly streamlined greenhouse + nose) probably actually does very well, and the MP4-12C setup of having side scoops feed radiators that vent to the wake is probably a lot better than having radiators in the front.
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Sure, the lack of plan taper doesn't explain all of it, but I would bet it's a significant factor. A perfect greenhouse taper won't do much for the car if the majority of the body terminates in a large wake area, which all these hypercars do. The departing angles are radically different on the lower-drag cars than the higher-drag cars. For the extreme eample, cf: XL1, which has as much greenhouse taper as the McLaren or Ferrari but a lower body taper to match which the latter cars lack. The trade-off is, it also has significantly narrower rear track, which would make a mid-engined RWD supercar so tail happy it would be nearly uncontrollable.
I guess my argument is that the basic shape has to be right or the car will never achieve low drag. The CLA is a good example of this: with the extra cooling inlets, wider tires, etc. it has a much higher drag coefficient even though the basic shape hasn't changed, but without the good shape it would not be able to achieve Cd .22 even with all the other details tuned in, and the AMG version drag would likely be even higher than it is.
Also, the Venom GT isn't just a bigger Exige body--it saw at least CFD development (there are images from some of those runs on the web), and I would suspect a wind tunnel at some point. With the active rear wing, that would be a necessity to get it to work correctly.